


Under the Moonlight

by cloud_dcst (greatcloudninja)



Series: TKS TsukaSen Week [7]
Category: Dr. STONE (Anime), Dr. STONE (Manga)
Genre: Canon Compliant, Discord: The Kingdom of Shipping (Dr. STONE), Dr. STONE Manga Spoilers, Explicit Sexual Content, First Time, Friends to Lovers, Love Confessions, M/M, Outdoor Sex, Stargazing, TKS TsukaSen Week - On a Boat, TKS TsukaSen Week - Stargazing, TKSevents, Tsukasen, sequel fic, tsktsukasenweekjan2021, tsusen, 司千
Language: English
Status: Completed
Published: 2021-01-30
Updated: 2021-01-30
Packaged: 2021-03-16 07:47:21
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,579
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/29078838
Author URL: https://archiveofourown.org/users/greatcloudninja/pseuds/cloud_dcst
Summary: It's late, and the noise and excitement on the deck of the Perseus hasn't stopped. Senku and Tsukasa can't sleep, so they seek a little peace and quiet at the back of the ship.Alone in the darkness, confessions are made and a friendship becomes something more.
Relationships: Ishigami Senkuu/Shishiou Tsukasa
Series: TKS TsukaSen Week [7]
Series URL: https://archiveofourown.org/series/2123469
Comments: 3
Kudos: 46
Collections: TsukaSen Week January 2021





	Under the Moonlight

**Author's Note:**

  * For [5Lifelines](https://archiveofourown.org/users/5Lifelines/gifts).



> This is my entry for Day 7 of [TKS TsukaSen Week](https://twitter.com/tksDCSTevents)! I used the prompts “Stargazing” and “On a Boat”!
> 
> This fic is also a sequel to my first ever TsukaSen fic [Turnabout is Fair Play](https://archiveofourown.org/works/23423182)! I've been planning to write this for a long time and I'm grateful that the TsukaSen Week event gave me the opportunity!

The drunken revelry on deck continued into the wee hours of the night. 

Senku couldn’t fault them for it. Tomorrow, they’d begin their hellish 40 day journey in earnest, so the crew of the  _ Perseus _ deserved this night of celebration and fun. After all, they wouldn’t have time to enjoy the casino and bar again until after they arrived in America.

It didn’t change the fact that Senku was trying to sleep, but the sounds from above were filtering into the sleeping cabin and keeping him awake. 

At least he wasn’t the only one trying and failing to sleep. Across the room. Senku could see Tsukasa had given up and was simply lying awake, squished into his little bunk. He’d changed out of his  _ Haute Couture Yuzuriha _ suit and was back in his normal clothes, as well. Something in Senku was a little disappointed to see it—and he resolutely ignored that thought. Nope, there was no reason for him to explore that line of thinking any farther at the moment. 

“Yo, Tsukasa. You wanna see if we can find a quieter spot to hang out for a while?” Senku called out to him. “Maybe if we head to the very aft of the ship, the sound of the engines churning the water will drown them out.”

There was relative silence in the cabin for several long moments—maybe Tsukasa actually  _ had _ fallen asleep and it just looked like he was still awake—but then his deep baritone met Senku’s ear. “I like that idea.”

“I thought you might. C’mon, let’s go.” Senku hopped out of his bunk and tugged on his shoes. Tsukasa, on the other hand, was still running around barefoot. Senku wasn’t sure why he noticed that, but he did.

The two left the cabin together and headed up toward the main deck. Luckily, the opening onto the deck was located behind Bar Francois and all of the action was in front of the bar, so there wasn’t anyone around when they got up there. The sounds that had been muffled, filtering into the sleeping cabin, were clear as day up on deck, though. “Is it just me, or are they even louder now than they were two hours ago?” Senku asked Tsukasa.

“I don’t think it’s just you,” Tsukasa replied in agreement. “The more they drink, the louder they seem to get.”

“Glad to know I’m not the only one who made that observation. Come on, let’s see if we can find somewhere that we can actually hear ourselves think.” With that, Senku headed off toward the back of the ship. He didn’t bother looking behind him to see if Tsukasa was following; Senku was highly aware of the presence of the taller male behind him. 

Thankfully, it seemed like Senku’s instincts were correct. As they traversed the length of the deck toward the back of the ship, the sound of rushing water seemed to overwhelm the dull roar of the party at the front. “Good, the engines seem to be in full working order,” Senku mused. “I’ll have to get Kaseki to check over them in the morning. We’re going to be pushing them to their limits to supplement the sails in order to make it to America in 40 days.”

“Mmn.” Tsukasa nodded in agreement. He was quiet, seeming almost contemplative as they approached the railing. Below them, the ocean was being churned white with foam as the ship traveled, as if the very sea itself was boiling. Oddly, the sight reminded Senku of the hot springs at Mount Hakone… and the day he’d died.

Tsukasa and Senku were both different people than they’d been that day. Senku had grown into a leader, a chief, and Tsukasa… well. He clearly still wasn’t  _ happy  _ about the idea of reviving every human on the planet. But his sister was alive, thanks to Senku, as was he himself after Hyouga’s betrayal. Senku had saved both of them.

And Senku loved him. The realization had been so simple, and yet completely overwhelming—the sky was blue, grass was green, and Senku had fallen in love with Tsukasa. Of course, he had realized it right after he’d put the man in the refrigerator, so he’d gone more than a full year without seeing him before they’d been able to bring home a medusa and revive him.

He hadn’t planned on confessing his feelings, not _ ever…  _ but then he’d gone and kissed Tsukasa impulsively earlier that night. Senku blamed Yuzuriha for making that outfit and for egging him on with the whole tie thing.

They still hadn’t talked about what had happened. Senku certainly wasn’t going to bring it up; so if Tsukasa didn’t, either, then that would be the end of it. And he was fine with that—chances were good Tsukasa was straight, anyway. He would probably be more interested in Minami than he would be in Senku. Tsukasa asking about whether Senku was flirting or scheming... that had just been him throwing Senku’s words back at him from way back when. It didn’t mean anything.

“You seem deep in thought about something.” Tsukasa’s voice cut through the still night air. “What is on your mind?”

Senku shook his head. “Nothing important. Just reminiscing.”

“What about?” Tsukasa turned to face Senku fully as he asked the question.

“About the day you killed me.” There was no reason to beat around the bush, not with Tsukasa. “And about the day I killed you.”

Tsukasa blinked. “What made you think of Hakone?” he asked quietly.

“I’m not sure, to be honest. Something about the ocean made me think of the hot springs. And from there my brain jumped to putting you in the refrigerator.”

“I see.” 

And that was that, Senku figured. Tsukasa had never been one to talk about emotions; he was much more focused on action.  _ What’s the situation, _ indeed. He looked back out over the water behind the ship, just enjoying the peace and relative quiet. The white noise of the engines, the whistling wind and foamy seas… it was relaxing.

“You know, I never actually gave you an honest answer.” Tsukasa’s words after another stretch of silence made Senku look up in confusion. “That day on the beach, when you asked if I was flirting or scheming. I  _ was _ scheming… but I was also desperately trying to hide the fact that I  _ wanted _ to flirt with you.”

“You— _ what?”  _ Senku’s eyes went wide at the confession. “You’re joking, right?”

“No. I wasn’t joking then, and I’m not joking now.” Tsukasa’s face was cast in shadow, the moon slightly behind him, but Senku could see the earnestness in his eyes. “It’s taken me a while to…  _ unlearn _ some of what I knew from the old world. I had to come to terms with some things about myself. But I don’t—I didn’t want to miss this chance to tell you. Not after what happened earlier.”

“You mean when I kissed you.”

“Yes. I thought… I mean, I assumed you weren’t interested in relationships in general, not just men. And after hearing the story of how you became village chief, I was even more convinced you were just…” Tsukasa trailed off.

“Asexual?”

“Yes.”

“The more accurate term for it is  _ demisexual.  _ In general, you’re right—I have no interest or attraction to most people in that way. But I can develop an interest… under the right circumstances. With the right person. If I’ve known someone for a long time, and we have a profound emotional bond.”

“Profound, hmm? That seems to be a pretty high bar to cross.”

“I don’t know. I think I’d say being killed by someone, going to war with them, saving their sister, fighting a traitor by their side, killing them, and bringing them back to life would count as a pretty  _ profound _ emotional bond.” 

Senku’s deadpan speech brought a chuckle from Tsukasa’s lips. “Then… you’re saying you’re attracted to me? You  _ were _ flirting earlier?”

“It’s a little deeper than that… but yes.”

“That’s good. Because I love you, Senku.” And with that, Tsukasa stepped closer to Senku and cupped his chin, bringing their lips together in a soft kiss. It was a far cry from the hurried mashing of lips Senku had given him earlier, but it stole Senku’s breath from his lungs with its tenderness. 

When they parted, he had to gasp for air. “What the hell…”

“Is something the matter?” Tsukasa’s expression morphed from happiness to concern in a split second.

Shaking his head, Senku leaned up on his tiptoes and pulled Tsukasa down into another kiss. This one was deeper, more hungry; Senku was in charge for all of a few seconds before Tsukasa realized what was going on and began to kiss back. Broad hands slid down to cup Senku’s hip and the small of his back. Tsukasa pulled him closer as his tongue slipped out to request entrance into Senku’s mouth. Senku moaned when he felt the hot tongue work its way inside. He tilted his head to the side so he could reach out with his own tongue, wanting nothing more in the moment than to explore Tsukasa’s mouth as well.

They stood there for a few minutes, just kissing each other. The  _ Perseus _ could have caught fire and Senku was certain neither of them would have noticed. But when they broke for air once again, Senku became very aware of his flushed cheeks and other more…  _ insistent  _ reactions to their embrace. Fortunately, it seemed Tsukasa was equally affected by their embrace.

"Senku…" Tsukasa's voice was deeper than usual, rumbling in a way that seemed to shake Senku to his very core. "I want you. Tonight."

He nodded in agreement before he could fully process what Tsukasa was asking. But once his brain caught up to his body's response, he knew it was the right one. "Yes. Please. I want it too."

"Do we need to go get supplies or anything? I can look for—"

Senku leaned up on his tiptoes and kissed Tsukasa into silence. "I have something we can use. We just need a place to lie down."

Without another word, Tsukasa reached up and unclasped his cloak, holding it up for inspection.

“Yeah, that’ll work.” Senku stepped back to let Tsukasa spread the thick leather over the deck. It looked like it would be just big enough for the two of them to lie on top of it. While he got it settled, Senku dug around in one of the pouches at his waist until he found a jar of thick salve he’d made prior to them leaving the village. It was something he’d come up with for the village fishermen, who often suffered from cracked and bleeding hands due to the rough ropes and nets, and he’d thought it would be handy to have extra for their voyage.

“It’s a good thing everyone’s busy,” he murmured as he began to strip out of his clothes.

Tsukasa nodded in agreement. “Yes… we should have plenty of privacy.” He couldn’t tear his eyes away from Senku as the shorter man unraveled the leather tie that kept his tunic closed. Moments later, Senku shrugged out of the tunic and his underskirt, leaving himself in nothing more than a tightly wound fundoshi that bulged lewdly in the front from his erection. “Oh…”

“Oh?” Senku looked up, only to realize Tsukasa was standing close enough that their bodies nearly touched. His breath caught in his throat at the dark, intense expression in Tsukasa’s amber eyes. Tsukasa wrapped his arms around Senku’s waist and lifted him into the air—a moment later, he found himself lying on top of the cloak on his back, head nestled on the fur around the collar as Tsukasa hovered above him. “Warn a guy before you go picking him up, yeah?”

“Sorry,” Tsukasa replied, not actually sounding sorry at all. He leaned down and pressed another kiss to Senku’s lips. “I’ll remember that next time.”

“You’d better.” Before Tsukasa could go too far, Senku pushed the small jar into his hands. “There. Use this.” 

“Got it.” Tsukasa set the jar aside before working on removing his own clothing. Unlike Senku, he was bare beneath the wrap he wore around his waist; Senku swallowed hard at the sight of Tsukasa’s thick erection. He’d seen Tsukasa naked before, of course, but… this was different. “May I?” Tsukasa’s fingers trailed over the thin fabric that strained to hold back Senku’s own hard cock.

Senku nodded mutely. With a gentle touch, Tsukasa slowly unwound the fabric until he could pull it away to leave the smaller man completely nude. The way he stared down at Senku made him shiver with anticipation—or maybe it was the cool breeze sending goosebumps all over his body. Either way, he murmured, “Are you going to stare all night, or are you gonna get on with it?”

“My apologies.” Tsukasa leaned forward and brushed one more kiss over Senku’s lips, which turned into two, and then more as Tsukasa opened the jar of salve. He slicked the fingers of one hand, using the other to lift Senku’s thigh and spread him open. A moment later the first finger slid inside.

Senku’s breath left him in a rush at the feeling of fullness. There was no pain, thanks to the salve, but even just one finger felt so… He was glad he’d experimented with his own fingers, because he knew that it would feel good in the end. “Can I move?” Tsukasa asked gently. Senku nodded and the finger withdrew partway, then slid back inside. Tsukasa kept his movements slow and gentle, working at the tight ring of muscle until Senku’s entrance loosened enough to add a second finger.

Tsukasa had worked Senku up to three fingers when his fingers brushed across  _ that _ spot. “N-naah!” The noise left Senku’s mouth in surprise. “Ts-Tsukasa, there!”

“Is that it?” Tsukasa asked. Senku nodded quickly. He was expecting Tsukasa to immediately target the area with firm prods, but he only teased at it occasionally. The pleasure built in slow waves as Tsukasa continued to work on stretching Senku’s entrance, peppering his face and neck with kisses.

By the time Tsukasa had his pinky inside Senku’s hole, a quiet whine slipped past his lips. “Tsukasa, please… fuck me already…” 

It seemed that was the sign Tsukasa had been looking for. “Of course,” he murmured. Tsukasa gave Senku’s prostate one more firm nudge for good measure before he withdrew his fingers. The feeling was enough to make him gasp, hips bucking from the shock of pleasure. His cock twitched hard and a gout of precum dribbled out over his stomach. Tsukasa’s lips curled into a grin at the sight as he used more salve to slick his own erection. Once he was ready, Tsukasa lifted Senku by the hips to align himself with the stretched and winking hole. 

“W-wait!” Senku cried out suddenly. Tsukasa paused, looking down at him as he pushed himself up into a sitting position. “This feels weird…”

“Do you want to stop?” Tsukasa asked, brow furrowing with concern, but Senku shook his head. He put a hand to Tsukasa’s chest and gently pushed him back until he was sitting on his heels. 

“It just felt… it felt like I wasn’t  _ doing _ anything,” Senku mumbled. “I want to…” He climbed into Tsukasa’s lap, legs spreading wide as he tried to position himself over Tsukasa’s erection. 

Tsukasa’s eyes widened as he realized what was going on. “Here, let me help…” He took over holding his own erection with one hand, the other getting a grasp of Senku’s hip. The smaller man braced himself on Tsukasa’s shoulders just before sinking down onto the thick, heavy length.

Senku’s head fell back and he cried out at the feeling of Tsukasa’s dick breaching his hole. It was  _ so big! _ Maybe it was the angle, but it felt even more massive than all four of Tsukasa’s fingers. And yet… Senku sank down on the length, more and more of it slowly working its way into his body. Every centimeter that filled him made the pleasure ratchet up, up, until he was panting and trembling. “Tsu— _ kaaaaah…” _ The name trailed off in a moan when he reached the base. 

Tsukasa didn’t seem to be faring much better. “Haah, Senku… you’re so tight…” His grip around Senku’s hip tightened; he struggled to hold himself back from just fucking up into the delicious heat. They sat there, both gasping for breath, waiting for Senku’s body to adjust to the feeling of being filled. 

After what felt like an eternity, Senku’s body finally relaxed a little. He wrapped his arms around Tsukasa’s neck and slowly lifted himself up, little by little, until about half of Tsukasa’s dick remained inside. Then he sank down once more, his hole swallowing the length. After a couple of false starts, he finally managed to get a rhythm going. 

“Fuck!” Tsukasa groaned as he pressed his face into the crook of Senku’s neck. Both of his hands wrapped around the slim waist, helping him along as Senku fucked himself. “Senku, you’re so hot inside. Does it feel good?”

Moaning under his breath, Senku nodded. “Yes… feels amazing…” Then he shifted his weight slightly and— “H-haah!” He cried out, hole twitching when the head of Tsukasa’s length made contact with Senku’s prostate. “There! Ts’kasa, p-please!”

It was enough to launch Tsukasa into action. His grip around Senku’s hips tightened as he leaned forward, pinning the smaller man to the cloak below them as he snapped his hips to fuck deep into Senku. Another cry escaped Senku’s lips as the new speed and angle drove him right to the brink of orgasm.

“Shit… Senku, I’m close!” Tsukasa groaned.

“Me too! Tsukasa! ‘K-Kasa, gonna— gonna—!” Senku couldn’t even finish speaking before his cock erupted, spilling ropes of cum over his stomach and chest. His hole clamped down on Tsukasa, which was enough to make him lose himself while buried deep inside. Senku moaned lowly at the feeling of being filled with cum.

The two slowly came down from their highs, panting for breath. Tsukasa pulled out of Senku’s ass with a groan, a dribble of cum following him out. “Sorry…”

“It’s fine…” Senku mumbled. His own cum was already cooling on his stomach from the ocean breeze, making him shiver. “I have a cloth in one of my bags, can you grab it?”

Nodding, Tsukasa leaned over where Senku had dropped his clothing. It took him a minute to find the right bag, but he withdrew a folded cloth and used it to wipe away as much of the cum from Senku’s body as he could.

The two were quiet as they dressed, the atmosphere feeling almost awkward somehow. Senku’s mind raced. What was next? Were they a couple now? How would this change their relationship?

_ Oh. _ The thoughts went still as Tsukasa pulled Senku into his arms, lying on the cloak. “Is this okay?” he murmured, breath warm against Senku’s ear. Tsukasa wrapped the edges of the cloak around them both; almost instantly, Senku felt warmer.

“This is great.” He rested his head on Tsukasa’s shoulder, sighing contentedly.

“Good. I was thinking we could do some stargazing before we head back. I never get tired of how beautiful the sky looks without all the light pollution we used to deal with.” Tsukasa smiled down at Senku, brushing a stray lock of his hair away from his face. 

“You know, I’ve been so busy these past few years, I don’t think I’ve really gotten to just stargaze,” Senku murmured. “Considering how obsessed I was with space as a kid, it’s kind of a shame. But there were always other things that were ten billion percent more important, and I would be so exhausted by nightfall that I wouldn’t be able to keep my eyes open.”

“Well, there’s no reason you can’t fall in love with it all over again, right?” Tsukasa asked. “We can do this whenever you want. Just say the word.”

“Alright. Let’s do it.”

The two of them shifted around a little until they both had a clear view of the sky above them. They spent the next half hour pointing out constellations, Senku telling Tsukasa the stories of the accompanying myths.

“Eventually we’re going to have to travel south of the equator,” Senku pointed out. “When we do, the constellations are going to change.”

Tsukasa nodded in agreement. “You’re right. I don’t actually know any of the southern hemisphere constellations. Do you?”

“I know a couple, but not many.”

“Then maybe we can come up with our own, and write our stories in the stars.”

“You sap,” Senku replied with a chuckle. “I didn’t expect you to be so poetic.”

“I suppose being with you is making me feel a little sappy,” Tsukasa conceded. 

Senku rolled his eyes, but leaned up to press a soft kiss to Tsukasa’s lips. “Me, too.” As he pulled away, he nearly cracked his jaw on a yawn. “It’s getting late. We should try to go back to bed.”

“Hmm… If you want to sleep, then sleep. I’ll carry you back to the cabin.”

Tsukasa’s offer was tempting… Senku nodded in agreement. “Okay.” He closed his eyes, scooting a little closer to Tsukasa under the cover of his cloak. 

The sound of his strong heartbeat lulled Senku to sleep within minutes.

**Author's Note:**

> Feel free to join the Dr. Stone shipping server! All ships are welcome!  
> We have lots of events scheduled, RP our fave ships, share headcanons, etc!  
> [Click here to join us!](https://discord.gg/RGy78Kj)


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